The present invention relates to an improvement in copy-productivity of an automatic duplex copying apparatus which reads both sides of a document and produces copies on both sides of a recording sheet.
As a device for reversing a document and thereby copying from both sides of the document, there has been known a reversible automatic document feeder (hereinafter referred to as RADF). When such a device is used, a large number of copies can easily be produced. Further, copies produced are in the same sequence as that of the documents, which eliminates the necessity of changing the sequence of produced copies.
Further, when interlocked with a sorter, collating and sorting by page can automatically be made and a large number of copies can be put in order accurately.
As a device wherein copies are produced automatically on both sides of a recording sheet through a single operation of a button, there has been known an ADF. When this unit is used, information on both sides of a document are copied onto both sides of a recording sheet, resulting in a saving of cost for recording sheets and easy filing. Further, it can be applied in many ways, including collecting materials in a booklet form for quick view.
When two-sided copying is made on a conventional automatic duplex copying apparatus, sheet refeeding from ADU (Automatic Duplex Unit) is started only after the detection of the stacked last recording sheet (having a copy only on one side) among the number of sheets set for 1st side copying.
The above-mentioned operations will, be explained as follows, referring to the line chart of FIG. 6. When a copy button is pressed (FIG. 6 (a)), sheet feeding for 1st side copying is made (FIG. 6 (b)). As an assumption for the explanation of the operations, a certain number of copies are set (hereinafter the number of copies set is called a set number of copying). When the first sheet of the recording sheets arrives at a photosensitive body, 1st side copying is started and the 1st side copying is continued until the set number of copying is completed. (FIG. 6 (c)). The recording sheets which have been finished in terms of 1st side copying are stacked in ADU (FIG. 6 (d)). After completion of stacking in the ADU, sheet aligning is made in ADU (FIG. 6 (e)). After completion of the sheet aligning, sheet refeeding from ADU is made (FIG. 6 (f)) and then 2nd side copying is made (FIG. 6 (g)).
According to the time chart for the foregoing, there is a period of time for the photosensitive body to wait (non-operation time) between the completion of 1st side copying and the start of 2nd side copying. Due to this standby period for a photoreceptor, it has been difficult to improve the copy-productivity for duplex copying.
Incidentally, though the ratio of the standby period to the copying time depends upon the set number of copying, it has been impeding the improvement of copy-productivity.
The present invention relates to a sheet feeding device for a sheet-shaped paper used for an image recording apparatus such as an electrophotographic copying machine and for a printing apparatus, and in particular, to the improvement of a sheet feeding device wherein a sheet-shaped paper ejected from the processing section is fed successively onto the top of a stack of paper loaded on a sheet tray while the bottom sheet of the aforesaid stacked paper is fed to the processing section, for example, a recording sheet recirculating feeder capable of having an automatic two-sided recording mode wherein images are recorded on both sides of a recording sheet, or an automatic multiple recording mode wherein multiple images are recorded on one side of a recording sheet, or the improvement of a sheet feeding device such as an automatic recirculating document handler wherein documents to be copied are fed in a circulating manner from the processing section to the document tray.
Generally, in an image recording apparatus such as an electrophotographic copying machine or in a printing apparatus, technologies for an automatic duplex copying apparatus capable of recording not only on one side but also on both sides of a recording sheet have been suggested. In conventional automatic duplex copying apparatus, a recording sheet, after being copied on one side, is held midway for a while, and fed again to the image-forming section. These technologies are disclosed in Japanese Patent Publication Open to Public Inspection Nos. 82247/1984, 114227/1984, 2241/1985 and 161641/1987 (hereinafter referred to as Japanese Patent O.P.I. Publication).
In such an automatic duplex copying apparatus, a recording sheet (a copy paper) copied on one side at an image-transfer section is turned and fed below the image-transfer section to be loaded on a stacker unit, and then the recording sheet is fed out and conveyed upward again and turned to be fed to the image-transfer section for copying on the other side of the recording sheet.
In a recording sheet feeder such as the aforesaid automatic two sided recording device, recording sheets fed successively to an intermediate tray need to be aligned accurately before they are conveyed to the image-forming section. When recording sheets are fed again to the image-forming section without being aligned accurately, conveyance trouble may take place, or when multiple recording is made on the obverse side of the recording sheet, registration error takes place between the first copied image and the second copied image and when recording on both sides of the recording sheet, registration error takes place between the copied image on the obverse side and that on the reverse side of the recording sheet.
In order to prevent the aforesaid registration error on the recording sheet, it is necessary to regulate both sides of each of the recording sheets conveyed and stacked on an intermediate tray and thereby prevent registration error for refeeding of sheets after an accurate sheet alignment.
When sheet width regulating members at both sides of an intermediate tray for regulating both sides of the recording sheet are provided at predetermined positions respectively for each recording sheet width, a recording sheet entering the intermediate tray, due to its direction being non-constant, hits the sheet width regulating member causing conveyance trouble, warping of the sheet and sheet irregularity including sheet skew. When the guide distance of the sheet width regulating member is broadened for preventing aforesaid troubles, sheet alignment fails to be stable.
In order to overcome these problems, it is desirable that one or both of sheet width regulating members are made to be movable and when the recording sheet enters an intermediate tray, the sheet width regulating members open up to make a slightly broader distance, and when recording sheets are stacked on the intermediate tray, sheet width regulating members move inward to slightly press both sides of the recording sheets for sheet alignment.
In prior art copying device as stated, a stack of recording sheets on a sheet tray (stacker) of the aforesaid ADU are subjected to sheet alignment after all recording sheets, each having been copied on its first side have been ejected from the main body of the copying device into an automatic duplex unit (ADU), and then sheet feeding is started after the completion of preparation for sheet feeding out and then the sheet is conveyed to aforesaid image-transfer section for forming a copied image on the second side of the recording sheet. Therefore, a certain period of time for preparation of switching has been needed between the completion of copying on the first side of the recording sheet and the start of copying on the second side thereof, resulting in the drop of copy-productivity.
Therefore, it is desirable to improve copy-productivity in the manner wherein the recording sheets are conveyed so that the recording sheets, each having been copied on its first side and stacked on the ADU may pass through the image-transfer section for the start of copying on the second side while the recording sheets, each having been copied on its first side, are being fed to the ADU from the image-transfer section.
However, the distance between the recording sheets adjoining each other for refeeding is changed by adjusting and controlling so that both sheet alignment and sheet refeeding may be conducted separately, because sheet refeeding and sheet alignment can not be made concurrently as disclosed in Japanese Patent O.P.I. Publication No. 161641/1987. Thus, in the prior art the change of distance between recording sheets adjoining each other has required a period of time and thereby the copy-productivity has been low.